Fabrication and Electrochemical Characterization of Freeze-Cast Tubular Solid Oxide Fuel Cells

Abstract

The use of freeze casting is suggested as a solution to significantly increase the volumetric power density of Tubular SOFCs (T-SOFCs) by enhancing gas diffusivity and triple phase boundary reactions. This paper reports the fabrication and characterization of freeze cast tubular anode supports for SOFCs. Tubular anode supports were fabricated using three methods: gelation casting, center pin method, and a freeze and drain method. A dual purpose freezing and drying chamber was designed and manufactured. The effects of slurry properties and process parameters were studied with respect to the resulting microstructures. The freeze and drain method was determined to be optimum for producing highly porous tubular anode supports with hierarchical, acicular or dendritic micro-pore channels. With an optimized freeze-drying cycle, drying time was reduced significantly with minimal residual moisture in the green bodies. Additionally, the electrochemical performance of the T-SOFCs with freeze cast anode was evaluated.

Tubular solid oxide fuel cells fabricated by a novel freeze casting method

“…In contrast, secondary drying involves removal of the unfrozen or bound solvent molecules at warmer temperatures, usually above the freezing point . For the complete removal of the frozen solvent from ceramic structures, freeze drying for one to several days has been a common practice . Thus, reduction in the freeze drying time, especially primary drying time, is a key factor to achieve a fast and competitive freeze casting process.…”

“…38,39 For the complete removal of the frozen solvent from ceramic structures, freeze drying for one to several days has been a common practice. 36,40,41 Thus, reduction in the freeze drying time, especially primary drying time, is a key factor to achieve a fast and competitive freeze casting process. Due to the confinement of the tube's exposed area inside of a mold during the freeze drying process, the removal of ice from the freeze-cast tubes is more challenging than that from the freeze-cast sheets or planar structures.…”

“…Recently, our group compared the microstructure of tubular anode supports fabricated by three different freeze casting methods: gel casting, center pin method, and freeze and drain method. 36 The preliminary results from that study suggested that the novel freeze and drain method is the most promising to fabricate tubular SOFCs with hierarchical and radially aligned pore channels. A detailed study was deemed necessary to improve the repeatability and shorten the turn-around time of the proposed method.…”

“…Although Moon et al fabricated tubular anode supports by freeze casting, they did not report further processing or electrochemical performance of functional tubular SOFCs. Recently, our group compared the microstructure of tubular anode supports fabricated by three different freeze casting methods: gel casting, center pin method, and freeze and drain method . The preliminary results from that study suggested that the novel freeze and drain method is the most promising to fabricate tubular SOFCs with hierarchical and radially aligned pore channels.…”

Fabrication of tubular solid oxide fuel cells by solvent‐assisted lamination and co‐firing a rolled multilayer tape cast

“…For example, Du and Finnerty created a spiral type of cell geometry and predicted a significant increase in volumetric power density . Different techniques have been used to fabricate tubular supports for SOFCs, including extrusion, pressing (compaction), slip casting, freeze casting, and dip coating . Extrusion is the traditional method of fabricating tubular SOFCs.…”